View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by HKU Scholars Hub Assessment of soil radon potential in Hong Kong, China, using a Title 10-point evaluation system Author(s) Tung, S; Leung, JKC; Jiao, JJ; Wiegand, J; Wartenberg, W Citation Environmental Earth Sciences, 2013, v. 68 n. 3, p. 679-689 Issued Date 2013 URL http://hdl.handle.net/10722/159517 Rights The original publication is available at www.springerlink.com Environ Earth Sci DOI 10.1007/s12665-012-1782-0 ORIGINAL ARTICLE Assessment of soil radon potential in Hong Kong, China, using a 10-point evaluation system S. Tung • J. K. C. Leung • J. J. Jiao • J. Wiegand • W. Wartenberg Received: 7 January 2011 / Accepted: 5 June 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com Abstract Radon and its progenies have been ranked developed in Germany (2005) to predict radon potential second of being responsible for lung cancer in humans. using both the in situ geogenic and geographic parameters Hong Kong has four major groups of uranium-rich plutonic under hierarchical ranking. Primarily, the ten-point system and volcanic rocks and is suffering from radon emanated requires the desk study of the geological environment of therefrom. However, there is a lack of radon potential maps sampling sites, which has an advantage of saving resources in Hong Kong to resolve the spatial distribution of radon- and manpower in extensive radon potential mapping over prone areas. A ten-point radon potential system was the traditional soil radon concentration sampling method. This paper presents a trial of radon potential mapping in Hong Kong to further verify the system. Despite some slight Electronic supplementary material The online version of this article (doi:10.1007/s12665-012-1782-0) contains supplementary departures, the system demonstrates an acceptable correla- material, which is available to authorized users. tion with soil radon concentrations (R2 = 0.62–0.66) from 768 samples of mainly intermediate radon potential. & S. Tung ( ) Hong Kong has a mean soil radon concentrations of Department of Physics, The University of Hong Kong, -3 Room 419, Chong Yuet Ming Physics Buliding, Pokfulam Road, 58.9 kBqm , while the radon potential from the ten-point Hong Kong, China system achieves an average of 4.93 out of 10 over the ter- e-mail: [email protected]; [email protected] ritory. The vicinity of fault zone showed high soil radon concentrations and potentials, which were conducive to J. K. C. Leung Department of Physics, The University of Hong Kong, uranium enrichment and rapid soil-gas diffusion near faults. Room 420, CYM Physics Building, Pokfulam Road, Hong Kong, High uranium-238 content in soil was found to cause high China soil radon concentration with a large R2, 0.84. The Jurassic e-mail: [email protected] granite and volcanic crystal tuff cover more than 85 % of J. J. Jiao the whole Hong Kong area, and they show relatively high Department of Earth Science, The University of Hong Kong, radon concentrations (Geometric mean 83 and 49 kBqm-3, Room 302, James Lee Building, Pokfulam Road, Hong Kong, respectively) which are associated with their high uranium China contents (Geometric mean 234 and 197 Bqkg-1, respec- e-mail: [email protected] tively). While indoor radon concentration is an important J. Wiegand factor for radon risk assessment, this study has not con- DMT GmbH & Co. KG Exploration & Geosurvey Division/ sidered the correlation between indoor radon concentration Geology and Borehole Survey, Am Technologiepark 1, and radon potential. The reason is that almost all buildings 45307 Essen, Germany e-mail: [email protected] in Hong Kong are high-rise buildings where indoor radon concentrations are governed only by the radium content in W. Wartenberg the building materials and the ventilation conditions. Department of Geoecology, Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Room 1. OG 115, Schleusenstr. 1, 26382 Wilhelmshaven, Germany Keywords Radon potential Á Radon concentration Á e-mail: [email protected] Faults Á Ten-point system Á Hong Kong 123 Environ Earth Sci Introduction A 10-point radon potential system Development of radon potential Wiegand (2001) proposed a 10-point radon potential sys- tem, which requires no measurement of soil radon con- Radon, in its metastable form, is the most abundant centration and permeability. On the contrary, the system radioactive gas in nature, to which human beings are involves the inspection of in situ geogenic and anthropo- mostly exposed. Radon and its progenies are together genic factors such as geology, relief, vegetation cover, ranked as the second highest cause of lung cancer mortality tectonics, soil sealing and traffic vibrations (Table 1). The (Darby et al. 2001). Indoor radon concentrations are usu- system enables radon potential more conveniently to be ally higher than atmospheric radon concentration by a assessed in anywhere once geological maps are available. factor of 10 in most countries and account for more than Those parameters can be studied on desk and the radon 50 % of total human exposure from natural radioactive potential can be estimated over a large area. Extensive sources (UNSCEAR 1994; Harley et al. 1988). mapping of radon potential across countries or even con- The relation between radionuclides in building materials tinents is facilitated under this system, which provides a and indoor ventilation conditions and the indoor radon prominent common ground for scientists to study radon concentration is revealed in different extents for high-rise potential (Wiegand 2005). buildings (Yu et al. 1996; Leung et al. 1998). On the In Table 1, the origin of soil is assessed and represented contrary, the soil-gas radon concentration, which generally by either ‘‘0’’ or ‘‘2’’ as a part of overall potential score ranges from several thousand or hundred thousand Bqm-3, (B10). The underlying rocks play a critical role in radon is proposed to be the major source of indoor radon for low- potential within natural soil. The rocks of higher uranium rise buildings (Kemski et al. 2001). The linkage between content, e.g. shale, granite and crystal tuff carry points as soil-gas and indoor radon concentration has been studied high as ‘‘3’’ whereas those low-uranium sandstones, con- heavily in the past decades, including a number of ana- glomerate and basalt carry ‘‘0’’. When the soil backfill is lytical and numerical radon entry models developed to [2 m, a higher probability of incorporated human distur- predict the indoor radon level from radon-bearing soil gas bance is expected and the type of backfill then becomes a (Gadgil 1992). Substantial works on, for example, radon key of radon potential. High-uranium backfills such as slag potential and radon index have been undertaken on iden- and ashes weigh 2 points while low-uranium sand and tifying soil-radon prone sites before applying any radon gravel carry zero point. On the one hand, the parameter entry models (Barnet et al. 2008; Kemski et al. 2009; ‘‘relief’’ accounts for the effect of the distribution of grain Wiegand 2001). Therefore, the development of a good size caused by erosion as well as soil development and the geogenic radon potential system is highly valued as long as impact of soil permeability along slopes on radon potential. the regional assessment of radon risk is demanded. The upper part of the hill favorable to radon emanation Kemski et al. (1996) suggested a radon ranking matrix by carries ‘‘1’’ point (Wiegand 2001). On the other hand, taking soil radon concentration and soil permeability into heavy vegetation carries ‘‘0’’ due to the exhaustion of soil account of radon potential. This system, however, is highly radon through transpiration, reduced soil moisture and affected by meteorological factors, particularly the variation increased soil permeability (Lewis and MacDonell 1990). of soil moisture conditions. USGS (1995) developed another Last but not least, the parameter ‘‘faults’’ is one of the system by accounting indoor radon, aerial radioactivity, major concerns in the local parameters. It carries ‘‘1’’ point geology, architecture type and soil permeability into radon as the possibly high soil moisture and vast uranium depo- potential. The system cannot provide any estimates when no sition near faults are in favor of radon emanation (Choubey houses are available in inspected areas. Collectively, the et al. 2000; Kemski et al. 1992; Wiegand 2001). As long as aforementioned two systems do not take the meteorological only the soil radon in rural/natural areas is concerned, the influence on soil permeability into account and hence may effect of traffic vibration and soil sealing are not considered involve uncertainties. For instance, the soil-gas radon con- in this study. centration can vary inversely with the soil permeability. Wiegand (2005) presented figures of soil radon potential Currently, most of the developed radon potential systems are and concentration mainly from Quaternary to Cretaceous thus based on soil-gas radon concentration and soil perme- materials in Germany from which there shows a strong ability as key parameters (Kemski et al. 2001; Reimer 1992; correlations (R2 = 0.94–0.99) between 10-point radon Buttafuoco et al. 2007). The accuracy of modern radon potential and the soil radon concentration (Bleile et al. potential maps would be improved but with limitation on 2005). In this study, the potential system was further ver- extent of mapping on the ground that experimental work ified in Hong Kong using the same instrumentation adopted involved in estimating these parameters often requires a by Wiegand. Hong Kong provides a reasonably desirable higher degree of knowledge and resources. ground for further testing the versatility of 10-point system 123 Environ Earth Sci Table 1 A ten-point radon potential system (Wiegand 2001) Parameter Classic RP Origin of soil (1) undisturbed soil or backfill \ 2 m (go to 2.1) 2 (2) backfill [ 2 (go to 2.2) 0 2.